The invention relates to a keyboard apparatus, and more particularly, to a keyboard apparatus which incorporates a plurality of overlays bound in the form of a book.
In applications such as inventory, input operation of Chinese characters or ticket reservation where a quantity of information must be processed, it is necessary for a keyboard apparatus used to input thousands or tens of thousands of information items. A typical apparatus includes a pair of keyboards juxtaposed to each other and between which a binder is fixedly mounted, with a plurality of overlays being coupled with the binder so as to permit any page to be opened over the respective keyboards. Each overlay is provided with a number of indicia such as the name of goods, flight numbers or the like at positions thereon which corresponds to individual key switches on each board. When an overlay of a given page assumes an open position over the keyboard, the indicia on that overlay provide a visual definition of corresponding key switches of the keyboard. A selection switch is provided to permit a distinction between the overlays so that when a particular overlay assumes an open position over the keyboard, a signal obtained from a particular key can be distinguished from a corresponding signal from the same key when another overlay is in its open position. Theoretically, this should enable an inputting operation of a quantity of information which corresponds to the product of the number of key switches actually provided, multiplied by the number of overlays.
The keyboard apparatus of this kind is disclosed, for example, in Japanese Patent Publication No. 24,306/1967 and U.S. Pat. No. 3,560,964 where the keyboard includes key jacks or key buttons. It will be seen that the number of keys which can be disposed on the keyboard is limited in view of practical manoeuvrability, and if it is desired to increase the number of information items which can be inputted, the number of overlays must be increased, with consequence that an extra time is needed to index a desired overlay. The number of keys which can be provided is also limited for the reason that each overlay is formed with apertures aligned with the individual key jacks or key buttons, so that there must be left a space between adjacent apertures to accommodate the indicia. The overlays used must be of a predetermined configuration or format, which causes inconvenience. The provision of a multiplicty of apertures in each overlay requires that it must be formed of a strong, thick material in order to provide the required mechanical strength. As will be seen, this imposes a limitation on the number of overlays which can be disposd on the keyboard. To overcome this difficulty, U.S. Pat. No. 3,560,964 proposes the use of interchangeable overlay units integral with binders, in combination with a selection switch for identifying the individual binders. However, the approach requires a troublesome handling and increases the overall cost.
On the other hand, the digitalization of the coordinates of a probe or pen located on a tablet is known, and a keyboard apparatus has been manufactured which operates on this principle for inputting a quantity of information items. In a keyboard apparatus of this kind, the surface of the tablet is functionally subdivided into segments so that each segment functions as an independent key. An overlay is disposed on the tablet and is marked with a multiplicity of indicia at positions corresponding to the individual key segments. One of the advantages of such keyboard apparatus is the elimination of the need for providing a space between adjacent keys since the indicia can be indicated directly above the respective keys. In this manner, a tablet of a standard size may be provided with nearly 3,000 keys, and the overlay used may be a sheet of paper of an ordinary quality. Recently, a keyboard apparatus is proposed which permits a selective, interchangeable use of a plurality of overlay sheets with a single tablet, thus substantially increasing the number of information items which can be inputted in a simple manner. However, the sheet construction of the overlays suffers from the handling difficulty in that each time an overlay is changed, it must be fixedly positioned on the tablet.